Chainsaws are potentially dangerous tools even when operators exercise extreme caution during their use. Over the years, chainsaws have been manufactured to include braking mechanisms that are intended to function to stop the rotation of the saw chain about the saw bar in the event that the saw bar and the chain thereabout kick backwards toward the operator. These “kickback” brakes operate either through centrifugal forces or through impact of a hand guard with the operator's support arm used to support and maneuver the chainsaw. In either case, the kickback brakes operate through the movement of various elements from active positions, where the saw chain is permitted to rotate about the saw bar, to brake positions, where the saw chain is braked. When the kickback brakes are activated, the saw chain is stopped through well-known typically spring biased mechanisms.
When kickback brakes are activated to stop the saw chain, they are typically activated when the operator is running the saw chain at full throttle. And the components of the chainsaw that engage to stop the saw chain do so while those components are driven at top speeds.
Chainsaws also typically operate in such a manner that the saw chain may continue to rotate about the saw bar when the operator has let up on the throttle. This is generally known as chain run down. And even when the throttle is fully released, there is a chance that the saw chain may be moving at a rate fast enough to be dangerous. Attempts have therefor been made to associate components of the braking mechanism with the throttle to brake the saw chain upon release of the throttle and release the saw chain from the braked state upon squeezing the throttle. It is believed that these attempts have failed because they provide a chainsaw having a throttle that is too difficult to squeeze and keep depressed, leading to great finger fatigue. These designs also hurt an operator's trigger finger when the kickback braking mechanism is activated. An example of such a chainsaw is provided in U.S. Pat. No. 4,683,660, wherein a link extends from components of the kickback braking mechanism to the throttle such that squeezing the throttle pulls on the braking mechanism to release its braking of the saw chain, and letting up on the throttle allows the braking mechanism to return to a position that stops the moving saw chain. Other chainsaw embodiments are provided in U.S. Pat. Nos. 4,594,780; 4,753,012; 5,813,123; and 6,842,987. In at least some of these prior art embodiments, the braking mechanism components are associated with the kickback brake, and, when the operator trips the kickback brake, the braking mechanisms force the throttle trigger to its normal non-squeezed position, causing the operator's finger to be uncomfortably forced open. This trigger kickback contributes to finger fatigue, which is a very big concern, particularly for professionals that must operate chainsaws for their maximum suggested running times.
Although the prior art has addressed the inherent dangers in operating a chainsaw and has provided mechanisms in an attempt to make chainsaw operation safer, a need still exists for new safety mechanisms that are more reliable and safe not only for the operator but for the chainsaw as well. A need exists to provide chainsaws that reduce chain run down. A further need exists for a chainsaw that brakes the saw chain upon release of the throttle trigger, but does not suffer from trigger kickback upon tripping the kickback brake.